Batteries are used to conserve and release energy that fuels our devices. In the case of smartphones, lithium-ion batteries are most commonly used.

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When the batteries charge, positively charged lithium ions move through an electrolyte and pass by a thin membrane (separator) onto a negative electrode, or anode. As the battery is discharged, lithium atoms oxidize and the resulting lithium ions travel back through the electrolyte onto a positive electrode, or cathode, while electrons travel via external circuitry, generating electric current.

Here’s a neat video explaining the entire process:

As you can see, there’s a lot of chemistry involved in the process of keeping your phone juiced up. But what may cause the battery to explode? It could be a couple of things. If metallic particles somehow end up in the electrolyte, they can align in such a way that they connect the cathode and anode, basically short-circuiting the battery and generating a lot of heat.

The battery can also get overcharged. This doesn’t happen in modern lithium-ion batteries, thanks to the overcharge protection mechanism that stops the charging process at full charge, but if it’s malfunctioning, the charging continues, causing the battery to heat up.

And last, the separator. As manufacturing processes improve, more power gets packed into smaller batteries, which requires separators to become thinner in order to provide better permeability and efficiency. It also increases the danger of separator breaching. A breached separator causes a battery to short-circuit, which in turn also generates a lot of heat.

Now, all that heat has to go somewhere. Since a battery is an isolated system, rising heat causes materials inside it to expand, further increasing the pressure and causing the visible “bloating” of the battery surface. Once the heat reaches a certain level, though, bad things start to happen.

The explosion and fiery bursts that follow are caused by so-called “thermal runaway.” This is a chain reaction of sorts, where the change in temperature causes a change in the system, which further increases the temperature, leading to a violent reaction.

In our case, once the heat has reached about 752 degrees Fahrenheit, metal oxide within the negative electrode of the battery will start releasing oxygen, which will fuel the fire within the enclosure of the battery. Oxygen will help the flammable electrolyte burn and expand, increasing the pressure within the battery until it finally explodes. All of this may happen in milliseconds and can cause burns and other injuries. Here’s what it looks like when a lithium-ion battery explodes:

Now, before you get scared, you should know that these events are rare and in most cases the internal battery mechanisms (overcharge, heat and short-circuit protection) are more than capable of protecting the battery. The smartphone circuitry also detects and does its best to protect the battery and the phone electronics from faulty chargers and irregularities in electric flow.

Still, accidents can happen — faulty batteries could be released by manufacturers without sufficient inspection, or it could be a user error, such as using a third-party charger or battery, which may not always be adequate for your device. A faulty charger may damage previously mentioned fail-safes on your smartphone and create conditions for a thermal runaway. A third-party battery may contain impurities that could cause it to short-circuit. Finally, the smartphone itself could be left in a hot environment, without an opportunity to cool off, resulting in an overheated battery.

So, remember to keep your device in optimal thermal conditions, unplug it after it has been charged (don’t leave it plugged in unattended!), and always remember to use batteries and chargers that are either sold or approved by the smartphone manufacturer.

Finally, technology is always advancing, and it’s worth mentioning that not all lithium-ion batteries react the same way when going through thermal runaway. Future developments are also promising, with solid-state lithium-ion batteries leading the way. They offer not only superior charging capabilities, but also increased safety, because they use solid electrolytes instead of liquid ones. Once scientists discover a solid electrolyte suitable for mass production, such batteries could very well replace the contemporary ones we all know and fear.

Have you ever experienced a lithium-ion battery explosion? Do you know someone who has? Please let me know in the comment section below.

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